In a conventional stamping and forming operation, strip material is fed through an operating zone between a punch assembly and a die assembly. The punch and die assemblies move relatively towards each other and the punch punches a hole in the strip and moves into a die opening in the die assembly. Thereafter, the punch assembly and die assembly move apart and the strip is again fed for the next operating cycle. It is also common practice to provide pilot pins on, or adjacent to, the punch assembly which enter previously provided pilot holes in the strip. The pilot pins precisely locate the strip in the operating zone of the machine so that the holes punched by the punches will be precisely located and/or any forming tools will engage the strip at a precisely predetermined position so that precisely dimensioned parts will be produced.
When the pilot pins and the punches move away from the strip after the punches have formed holes therein, there is often times a tendency for the strip material to move with the punches and/or the pilot pins laterally of the plane occupied by the strip in the center of the operating zone of the machine. Such movement of the strip results from the fact that the pilot holes will have a diameter only slightly greater than the diameter of the pilot pins and the holes produced by the punching operation will be only very slightly larger than the punches themselves. The friction developed between the punches and pilot pins and the strip therefore prevents the strip from remaining stationary when the punches and pilot pins are withdrawn and it tends to be dragged for a short distance with the punches and pilot pins when the punch assembly is moved from its closed position to its retracted or open position.
In order to overcome the problem discussed above, it is common practice in conventional stamping and forming machines to provide a stripping mechanism which restrains the movement of the strip when the punch assembly moves away from the strip to its open position. Where the machine has a conventional punch and die assembly comprising spaced apart die shoes which have the punches and dies mounted therein, it is common to provide a spring loaded rod or the like which bears against the strip and which is constructed such that when the die shoes move relatively towards each other, the spring which biases the rod is compressed. When the die shoes move relatively away from each other, the rod remains against the strip while the punches and pilot pins move away from the strip thus restraining the strip against movement and stripping the material from the pilot pins and the punches.
U.S. Pat. No. 4,497,196 discloses a stamping and forming machine in which the punches and dies are mounted on opposed spaced apart tooling assemblies which move relatively towards and away from each other during each operating cycle. For several reasons, conventional known types of stripping mechanisms are not practical for machines of the general type described in that patent. For example, both the die assembly and the punch assembly move during an operating cycle towards and away from each other between an open position and a closed position. The total stroke is thus the sum of the displacements of both of the tooling assemblies and the stroke of the punch assembly itself is therefore considerably smaller than the stroke of a conventional machine in which only the upper die shoe or the punch assembly moves. Additionally, machines of the type described in U.S. Pat. No. 4,497,196 are extremely compact and it is impractical to provide conventional stripping devices for the reason that there is simply not sufficient space to permit their inclusion.
The present invention is directed to the achievement of an improved stock retaining and stripping means which can be used to advantage on many types of stamping and forming machines and which is particularly adapted for use on machines of the general type described in U.S. Pat. No. 4,497,196 (which is hereby incorporated by reference in its entirety).